Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$5.45	12.710%	$6.1427	$6.14	$6.15	$6.10
Purchase #2	$116.60	9.588%	$127.7796	$127.78	$127.80	$127.80
Purchase #3	$185.72	12.244%	$208.4596	$208.46	$208.45	$208.50
Purchase #4	$45.68	13.441%	$51.8198	$51.82	$51.80	$51.80
Purchase #5	$152.75	6.657%	$162.9186	$162.92	$162.90	$162.90
Purchase #6	$115.47	7.332%	$123.9363	$123.94	$123.95	$123.90
Purchase #7	$161.47	12.103%	$181.0127	$181.01	$181.00	$181.00
7 purchase totals =	$783.14		$862.0693	$862.07	$862.05	$862.00